1. Field of the Invention
This invention relates to a device for correcting a tremble of a focused image of an object caused by an oscillation of an optical device due to, for example, a hand tremble.
2. Description of the Related Art
Usually, an optical device is provided with a device for correcting a tremble of an focused image. The device for correcting the tremble includes a sensor of angular speed, and a correcting optical system which is placed on an optical path of a photographing optical system of the optical device. An amount of trembling of the optical device is calculated by integrating a signal output from the sensor of angular speed. The correcting optical system is driven so that the tremble of the focused image, caused by an oscillation of the optical device, is canceled.
Accordingly, a movement of an object image on, for example, a surface of a camera film and a light receiving surface of photoelectric conversion element is corrected. Namely, the focused image tremble of the object is corrected. In practice, due to a frequency characteristic of the driving device of the correcting optical system, the movement of the correcting optical system follows the focused image tremble, being shifted by a predetermined phase.
Therefore, when the frequency of the focused image tremble becomes high, a phase delay is generated between the focused image tremble and the drive of the correcting optical system, so that the response characteristic of the correcting optical system becomes comparatively slow. Due to the comparative slowness of the correcting optical system in responding to the focused image tremble, the correcting optical system may be driven in an opposite direction to a direction in which the correcting optical system should be driven in order to respond to the focused image tremble. Accordingly, the focused image tremble becomes larger than when the device for correcting the focused image tremble is not operated.
For example, when a camera is fixed on a tripod for photographing and a shutter button is pressed, the tripod is trembled in accordance with an oscillation of a release shock, by pressing the shutter button. The release shock is transmitted to the camera, after being amplified. Accordingly, if the correcting operation of the focused image tremble is performed when the camera is fixed on the tripod, the focused image tremble is amplified by the above mentioned movement of the correcting optical system, so that a picture quality of a photographed image is lowered.
Therefore, an object of the present invention is to provide a device for correcting the focused image tremble, which can be controlled in accordance with a frequency of the tremble. Another object of the present invention is to provide a camera, provided with the correcting device.
In accordance with an aspect of the present invention, there is provided a device for correcting a tremble of a focused image comprising: a tremble detector that detects a tremble of optical axes of an optical device; correction optical systems that correct the tremble of the optical axis; driving devices that drive the correction optical systems; a controlling system that controls the driving devices in such a manner that a tremble of a focused image of an object due to the tremble can be canceled; a reverse detector that detects a reverse of a direction of the optical axes tremble, detection of the reverse detector being repeatedly performed at a predetermined time interval; and a measuring system that measures a time interval, from a previous moment at which the reverse was detected, to a present moment at which the reverse is detected.
In the correction device, the controlling system stops the driving devices if the time interval is shorter than a predetermined value. The predetermined value is set to approximately 25 milliseconds.
Preferably, the correcting device further comprises a tremble-direction-memorizing-system that judges a direction of the tremble by comparing a previous amount of the tremble at the previous moment and a present amount of the tremble at the present moment, and memorizes the direction. In the correcting device, when a present direction of the tremble judged at the present moment by the tremble-direction-memorizing-system is different from a previous direction of the tremble judged at the previous moment by the tremble-direction-memorizing-system, a reverse of the direction of the tremble is detected.
Preferably, the tremble-direction-memorizing-system judges the direction of the tremble by detecting an increase and a decrease between the previous amount and the present amount.
Preferably, the tremble detector can detect the tremble of the optical axis along two axes, and when the time interval, measured by the measuring system based on the result of detection of the reverse detector, is less than a predetermined value with respect to one axis of the two axes, the controlling system stops the correcting operation with respect to the two axes.
In accordance with another aspect of the present invention, there is provided a camera which is provided with a device for correcting a tremble of a focused image comprising: a photographing optical system; a tremble detector that detects a tremble of an optical axis of the photographing optical system; a correction optical system that corrects the tremble of the optical axis; a driving device that drives the correction optical system; a photographing controlling system that records an image of the object, controlling an image capturing operation; a tremble correction controlling system that controls the driving device in such a manner that a tremble of a focused image of an object due to the tremble can be canceled; a reverse detector that detects a reverse of a direction of the optical axis tremble, detection of the reverse detector being repeatedly performed at a predetermined time interval; and a measuring system that measures a time interval, from a previous moment at which the reverse was detected, to a present moment at which the reverse is detected.
In the camera, the tremble correction controlling system stops the driving device if the time interval is shorter than a predetermined value. Preferably, the predetermined value is set to approximately 25 milliseconds.
Preferably, in the camera, only while the image capturing operation is being carried out, the reverse detection by the reverse detector, the measuring of the interval by the measuring system, and the stopping operation of the driving device by the tremble correction controlling system are carried out.
Preferably, the camera further comprises a tremble-direction-memorizing-system that judges a direction of the tremble by comparing a previous amount of the tremble at the previous moment and a present amount of the tremble at the present moment, and memorizes the direction. In the camera, when a present direction of the tremble judged at the present moment by the tremble-direction-memorizing-system is different from a previous direction of the tremble judged at the previous moment by the tremble-direction-memorizing-system, a reverse of the direction of the tremble is detected.
Preferably, the tremble-direction-memorizing-system judges the direction of the tremble by detecting an increase and a decrease between the previous amount and the present amount.
Preferably, in the camera, the tremble detector can detect the tremble of the optical axis along two axes, and when the time interval, measured by the measuring system based on the result of detection of the reverse detector, is less than a predetermined value with respect to one axis of the two axes, the controlling system stops the correcting operation with respect to the two axes.